The quantum spatial coherence properties of stimulated Raman scattering

Thesis (Ph. D.)--University of Rochester. College of Engineering and Applied Science. Institute of Optics, 1991.Stimulated Raman scattering (SRS) exhibits fluctuations in macroscopically observable quantities that arise from microscopic quantum mechanical uncertainty. The spatial fluctuations in SRS are affected by the gain-guided medium in which light propagates, and are important for characterizing the spatial coherence properties of SRS as a light source. In this thesis, the spatial coherence properties of SRS are examined both theoretically and experimentally. A transient, 3-D solution incorporating the excess-noise effect of gain-guided amplifiers is developed. The excess-noise effect associated with the non-orthogonal spatial modes is common to all gain-guided media and other non-hermitian optical systems. The solution is applied to transient SRS to study the beam-pointing-angle fluctuations in SRS. The beam-pointing-angle fluctuation is the result of the superposition of spatial modes that are randomly excited by quantum noise. This fluctuation represents a quantum-noise-limited directional instability for spontaneously generated light sources. Two experiments are conducted. The first one is to study the connection between quantum mechanical uncertainty and macroscopic fluctuations. The second one is to compare quantitatively the beam-pointing fluctuations of the Stokes field with predictions from the theory developed in this thesis and a theory that does not include excess-noise. It is shown by the first experiment that the phases of the macroscopic Stokes field, which originated from quantum noise, are random. This complements previous studies on the pulse-energy statistics of the Stokes field, and verifies the thermal-like characteristics of Stokes light generated under unsaturated gain conditions. This experiment demonstrates single-shot, second-order, spatial interference of light from two independent, thermal-like sources. The second experiment measures the beam-pointing angles in various interaction geometries. The beam-pointing fluctuations of Raman generators are smaller than that predicted for light propagating in free space, but agree reasonably well with the predictions of the new theory. The transient solution can also be applied to study other spatial fluctuations such as the Poynting vector where the excess-noise effect is more prominent